This is related to solid or perforated steel belts only. Wire mesh is a different topic
A steel belt for baking is made from hardened and tempered carbon steel. It can be solid or perforated, depending on product to be baked. The belt surface, the baking surface, is covered with a thin bluish/blackish layer achieved during the heat treatment procedure. This makes the bake oven belt surface hard, smooth and basically easy to clean and to release product from.
Before a steel belt is put to work for the first time it should be carefully cleaned from its protective oil (factory protected with a food grade oil as last production step, to prevent corrosion.)
When the belt is cleaned and runs well in oven both in cold and warm conditions the surface should be polished with preferably bees wax to get a perfect shiny and black surface. Depending on product to bake, different release agents can be used to prevent product from sticking. As you know there are a lot of different brands on the market and you just need to find something that fits your process well.
When replacing a belt in an old oven special measures has to be taken regarding cleaning of oven components.
There are a few different ways to clean a bake oven belt during production (baking). Normally a rotating brush is run at the return stand after the discharge drum, when the belt still is hot. A roller cross the width keeps the pressure constant on the backside of belt over the brush. Important is to have the drive of the brush electrically connected to the belt drive. The cleaning roll should never ever be allowed to run without the belt is moving. The rotation direction of brush should be with the belt direction.
If a perforated steel belt is used the cleaning brush should not be driven. Only by the movement of the belt.
The brush cleaning can take place all the time, in cycles or when needed. This depends on the grade of contamination.
Some ovens are equipped with scrapers instead of brushes. Important is to have a metal grade that do not harm the steel belt and its oxide layer.
Sometimes it can be good to use a felt pad or a soft scraping with a collect pan after the cleaning station, to pick up debris. If not enough, several cleaning pads can be put in a raw.
As said above, the steel belt have a hard, smooth, dirt resistant surface when new. On older baking lines you can have worn steel belts for different reasons. If support roller(s) are “frozen” (not rotating) on return stand they will quickly start to wear on the belt surface and destroy the oxide on belt.
All of these rollers needs to be inspected and cleaned as well. Same thing with break point rollers or tracking rollers in contact with the bake oven belt surface.
Cleaning rollers or scrapers can be used to often or be tensioned to hard against the belt surface. Doctor blades or scrapers for releasing products can be harming the belt surface as well, sometimes because of too hard material, sometimes because of sharp angle or something stuck between belt and knife.
A common product like NaCl will act like grinding paste on your steel belt for sure, when stuck under a scraper
So therefore it is of outmost importance to inspect the belt surface often. Especially when cleaning efforts takes place. If shiny areas occur, it’s needed to right away find out from where they come.
Remember that a “frozen roller” has to be replaced. ASAP.
The belt should always be covered with oil/fat also when not in use. A dry belt will corrode very fast.
Good housekeeping is , as always, the best insurance.
But before anything else you should ask yourself and your colleagues; Was this problem always present? Was something ever changed regarding the baking process? (temperature, speed, brand of ingredients, sugar content VS flour and shortening, etc.)